1. Field of the Disclosure
This disclosure relates to a liquid crystal display device adapted to prevent the generation of noise, and a driving method thereof.
2. Description of the Related Art
The application fields of liquid crystal display (LCD) devices are expanding due to desirable features such as light weight, slimness, and low driving voltage. This trend is evident in the ways in which the LCD devices are being applied to office automation equipment, audio equipment, video equipment, and so on.
An LCD device controls the light transmission of liquid crystal in a state between liquid (or isotropic) and crystalline in accordance with an applied voltage and converts an electric signal into visual information, in order to display an image. To this end, the LCD device includes two substrates having electrodes and a liquid crystal layer interposed between the substrates. Such an LCD device is light weight and has a small volume and is driven by low electric power, in comparison with other display devices of the same size.
The LCD device selectively transmits light emitted from a light source in its rear side portion using pixels on a liquid crystal panel in its front side portion, thereby displaying an image. In other words, the LCD device controls the intensity of light from the light source, unlike a cathode ray tube (CRT) of the related art, which adjusts the intensity of cathode rays in order to display an image.
FIG. 1 is an equivalent circuit diagram showing a pixel on an LCD device of the related art. As shown in FIG. 1, a pixel of the related art LCD device includes a thin film transistor TFT at an intersection of gate and data lines GL1 and DL1 and a storage capacitor Cst connected parallel to a liquid crystal cell Clc. The storage capacitor Cst maintains a data voltage charged into the liquid crystal cell Clc.
The related art LCD device with such a pixel is generally driven in an inversion system which forces a polarity inversion of a desired format, thereby reducing the deterioration of liquid crystal. The inversion system is classified as a frame inversion system, a line inversion system, a dot inversion system, or other systems according to the desired formats.
FIG. 2 is a view explaining a horizontal 2-dot and vertical 2-dot inversion system applied to the related art LCD device. FIG. 3 is a view showing a specific pattern of vertically arranged white-black (hereinafter, a vertical alternating white-black pattern). FIG. 4 is a waveform diagram showing a data voltage applied from the first data line DL1 to the liquid crystal cells when the vertical alternating white-black pattern is displayed.
As shown in FIGS. 2 through 4, when the related art LCD device is driven in the horizontal 2-dot and vertical 2-dot inversion system and the vertical alternating white-black pattern is displayed in which a black gray-scale B and a white gray-scale W are arranged to alternate with each other in three lines, noise is generated from the related art LCD device.
In order to drive the LCD device in the horizontal 2-dot and vertical 2-dot inversion system, a polarity control signal POL which enables data voltages to be inverted every 2 pixels in both horizontal and vertical directions is previously provided.
When the LCD device driven in the horizontal 2-dot and vertical 2-dot inversion system displays the vertical alternating white-black pattern in which three lines of the black gray-scale B and three lines of the white gray-scale W alternate with each other, the black gray-scale data voltages applied to the liquid crystal cells on a second line L2 and a third line L3 of the vertical direction have contrary polarities.
As such, the voltage difference between a positive black gray-scale data voltage +B and a negative black gray-scale data voltage −B becomes greater in a polarity inversion interval S including the second and third lines L2 and L3. Therefore, the related art LCD device causes elements included in a drive circuit of the liquid crystal cells to tremble (or vibrate). In this case, the difference between positive and negative voltage levels for the black gray-scale is established to have a relatively large value, while the voltage difference between positive and negative data voltages for the white gray-scale is established to have a relatively small value.
In other words, when a specific pattern is displayed in which at least three lines of black gray-scale and at least three lines of white gray-scale alternate with each other, the related art LCD device causes circuit elements (for example, a capacitor) driving the liquid crystal cells to tremble (or vibrate) during the polarity inversion interval S which allows black gray-scale data voltage with a large difference of positive and negative voltage levels to be polarity-inverted. As a result, the disadvantage of such a device is the generation of noise.